1. Field of the Invention
This invention relates to a chain pulling device for a roller shaft for roller blinds or screens, comprising a housing, a chain pulley provided with a central channel and a series of notches at the periphery and situated in the housing, and a chain slung around the pulley.
2. Description of the Prior Art
U.S. Pat. No. 4,448,233 discloses a pulling device of this type which comprises a cord pulley situated in a housing and a clamp disposed in a chamber in said housing and about said cord, said clamp becomes operative when turning the cord pulley by the weight of the blind or screen. This pulley device cannot be used with a chain, and even with a cord the clamp is ineffective since the cord will slip sometimes over said clamp.